Wire-based calibration apparatus for X-ray imaging systems

Abstract

A calibration target for use with a radiographic image detector includes a target body securable to the image detector and a plurality of radiopaque linear markers, e.g. wires, fixed to the target body, wherein access to the image detector by incident radiation is at least partially blocked by the plurality of linear markers. By using the geometric properties of wires and advanced detection techniques, a precise calibration suitable for high-quality, volumetric three-dimensional CT reconstruction from biplanar X-ray images is achieved.

What is claimed is: 
     
         1 . A calibration target apparatus for use with a radiographic image detector of an imaging system, the calibration target comprising:
 a target frame securable to a radiographic image, the target frame defining an interior passage; and   a plurality of at least partially radiopaque markers coupled to the target frame and transversing the interior passage,   wherein the plurality of radiopaque markers partially obstruct passage of radiation through the internal passage of the frame.   
     
     
         2 . The apparatus of  claim 1 , wherein the plurality of radiopaque markers are linear in shape. 
     
     
         3 . The apparatus of  claim 1 , wherein the interior passage has a generally circular shape. 
     
     
         4 . The apparatus of  claim 1 , wherein the plurality of radiopaque markers have known spatial coordinates relative to the target frame. 
     
     
         5 . The apparatus of  claim 1 , wherein the target frame comprises a pair of frames secured together by posts. 
     
     
         6 . The apparatus of  claim 1 , wherein the target frame further comprises a pair of brackets for securing the target frame to the radiographic image detector. 
     
     
         7 . The apparatus of  claim 1 , wherein a first of the plurality of radiopaque markers are attached to the target frame at a first depth of the interior passage and a second of the plurality of radiopaque markers are attached to the target frame at a second depth of the interior passage. 
     
     
         8 . The apparatus of  claim 1 , further comprising:
 a side wall encompassing the target frame.   
     
     
         9 . The apparatus of  claim 2 , wherein the plurality of radiopaque markers comprise wires. 
     
     
         10 . The apparatus of  claim 8 , further comprising:
 a reference marker having a unique shape disposed on the sidewall.   
     
     
         11 . The apparatus of  claim 8 , wherein the target frame has a size and shape to enable frictional attachment over the radiographic image detector. 
     
     
         12 . The apparatus of  claim 10 , further comprising:
 plurality of reference markers, each having a unique shape, disposed on the sidewall.   
     
     
         13 . The reference apparatus of  claim 12 , wherein the respective shapes of the plurality of reference markers collectively comprise an asymmetric pattern. 
     
     
         14 . A calibration target for use with a radiographic image detector comprising:
 a target body securable to the radiographic image detector, the target body defining an interior passage; and   a plurality of at least partially radiopaque linear markers fixed to the target body and transversing the interior passage,   wherein the plurality of at least partially radiopaque linear markers obstruct passage of radiation through the internal passage of the target body.   
     
     
         15 . The calibration target of  claim 14 , wherein the plurality of at least partially radiographic linear markers have known spatial coordinates relative to the target body. 
     
     
         16 . The calibration target of  claim 14 , wherein the plurality of radiopaque markers comprise wires. 
     
     
         17 . The calibration target of  claim 14 , wherein the target body is defined by a side wall. 
     
     
         18 . The calibration target of  claim 14 , wherein the target body has a substantially circular or rectangular exterior perimeter. 
     
     
         19 . The calibration target of  claim 14 , wherein the target body has an end surface comprising a material that is substantially transparent to radiation incident thereon. 
     
     
         20 . The calibration target of  claim 17 , further comprising:
 a reference marker disposed on the sidewall.   
     
     
         21 . The calibration target of  claim 20 , further comprising:
 plurality of reference markers disposed on the sidewall.   
     
     
         22 . The calibration target of  claim 21 , wherein the plurality of reference markers collectively comprise an asymmetric pattern. 
     
     
         23 . A calibration target for use with a radiographic image detector comprising:
 a target body securable to the radiographic image detector, the target body defining an interior passage; and   a plurality of at least partially radiopaque non-spherical markers fixed to the target body and transversing the interior passage,   wherein the plurality of at least partially radiopaque non-spherical markers obstruct passage of radiation through the internal passage of the target body.   
     
     
         24 . The apparatus of  claim 23 , wherein the plurality of non-spherical markers have known spatial coordinates relative to the target body. 
     
     
         25 . The apparatus of  claim 24 , wherein the plurality of non-spherical markers comprise wires.